A Standardized Protocol for Measuring Bioelectrical Impedance in Green Turtles (Chelonia mydas)

• Published in: Physiological and biochemical zoology Vol. 96; no. 2; pp. 87 - 99
• Main Authors: Kophamel, Sara, Ward, Leigh C., Ariel, Ellen, Mendez, Diana, O’Brien, Lauren M., Burchell, Lauren, Munns, Suzanne L.
• Format: Journal Article
• Language: English
• Published: United States The University of Chicago Press 01.03.2023
• Subjects: Animals; Body Composition; Electric Impedance; Reproducibility of Results; Turtles; Water; bioelectrical impedance spectroscopy; sea turtles; bioelectrical impedance analysis (BIA); temperature; reptile; postprandial state; resistance
• ISSN: 1522-2152; 1537-5293
• DOI: 10.1086/722451

Bioelectrical impedance analysis (BIA) is gaining popularity in wildlife studies as a portable technology for immediate and nondestructive predictions of body composition components, such as fat-free and fat masses. Successful application of BIA for field-based research requires the identification and control of potential sources of error, as well as the creation of and adherence to a standardized protocol for measurement. The aim of our study was to determine sources of error and to provide a standardization protocol to improve measurement precision of BIA on juvenile green turtles (Chelonia mydas; n=35). We assessed the effects of altered environmental temperature (20°C–30°C), postprandial state (2–72 h), and time out of the water (2 h) on five impedance parameters (resistance at infinite frequency [Rinf], resistance at zero frequency [R0], resistance at 50 kHz [R50], phase angle at 50 kHz [PhA50], and intracellular resistance [Ri]) using a bioimpedance spectroscopy device. Technical reproducibility of measurements and interanimal variability were also assessed. We found an inverse exponential relationship between change in environmental temperature and impedance parameters Rinf, R0, and R50. Postprandial state significantly increased Rinf and Ri 72 h after feeding. BIA measurements were reproducible within individual juvenile green turtles at temperatures from 20°C to 30°C. Significant variation in impedance values was found between animals at all temperatures, sampling times, and postprandial states, but the relative differences (%) were small in magnitude. Our study suggests that measurement precision is improved by measuring animals at consistent environmental temperatures close to their preferred thermal range. We propose a standardized protocol of measurement conditions to facilitate laboratory and field use of BIA for body composition assessment studies in turtles.